1. Field of the Invention
The present invention relates to solar sensitizers using heteroleptic, dual tridentate Ru(II) complexes and dye-sensitized solar cells, particularly to sensitizers and dye-sensitized solar cells with better conversion efficiency.
2. Description of the Prior Art
Petrochemical fuel is a nonrenewable energy source and might possibly run out very soon. In addition, burning petrochemical fuel results in excessive CO2 exhausts which not only pollute the atmosphere, but also become one of the primary causes of global warming. Therefore, searching for alternative energy supplies to reduce reliance on petrochemical fuels is a subject of great urgency.
During the development of green energy, it is found that solar energy is the cleanest, most abundant and requires neither mining nor refinement. Solar energy, therefore, becomes the most promising technology among the current development and search for new energy. The manufacturing process of a dye-sensitized solar cell (DSSC) is simple and the associated fabrication cost is also significantly lower than that of a silicon-based solar cell of prior arts. Therefore, DSSC has been regarded as one of the most notable solar cell technologies following silicon-based solar cells. Because the intrinsic properties of photosensitizers directly affect the photoelectric conversion efficiency of a DSSC, the photosensitizers therefore becomes one of key issues while conducting research on DSSCs.
A N719 dye and black dye (N749 dye) are photosensitizers commonly used at present, which comprises the structure shown in following formulae. However, the conventional N719 and N749 dyes possess two and three monodentate NCS− (thiocyanate) ligands, which are considered to be the weakest coordination ligands of the whole molecule, and can be easily replaced by other donor fragments in the electrolyte solution of DSSCs. Therefore, replacing NCS− ligands with other stronger coordinated chelates or chromophoric ligands would allow significant increase of efficiency and life-expectancy of DSSCs.

To sum up the foregoing descriptions, the photoelectric conversion efficiency of a DSSC is directly dependent on the inherent property of photosensitizer; therefore, developing photosensitizers with decent photoelectric conversion efficiency is an important goal to be achieved.